NTP: ntpdc: Failed to Get System Info from NTP Daemon

This error is normally observed when attempting to start sfptpd in one of the supported PTP and NTP/NTP fallback modes:

warning: ntpdc: failed to get system info from NTP daemon, Connection timed out
error: timed-out retrieving NTP system info. Is ntpdate running?
critical: failed to create ntp module, Connection timed out

The error occurs because on startup, sfptpd will attempt to communicate with ntpdc on the local loopback interface.

1. Check that a loopback interface config file exists in /etc/sysconfig/network-scripts/ifcfg-lo. The file would normally contain the following lines:

   DEVICE=lo
   IPADDR=127.0.0.1
   NETMASK=255.0.0.0
   NETWORK=127.0.0.0
   # If you're having problems with gated making 127.0.0.0/8 a martian,
   # you can change this to something else (255.255.255.255, for example)
   BROADCAST=127.255.255.255
   ONBOOT=yes
   NAME=loopback

2. Check that the following line is enabled in the /etc/ntp.conf file:

   # Permit all access over the loopback interface.  This could
   # be tightened as well, but to do so would effect some of
   # the administrative functions.
   restrict 127.0.0.1

   This could also be a different form:

   interface listen 127.0.0.1

3. On some OSs it might be necessary to explicitly enable NTP mode 7 to allow communication with ntpdc/ntpd. This is done by adding the following line anywhere in the /etc/ntp.conf file:

   enable mode7

   Note: There is no space between mode and 7.